Control method and controller of program suspending and resuming for memory

ABSTRACT

A control method, for a memory array, the control method comprises programming the bit-cell of the memory array in a programming stage; and discharging the bit-cell of the memory array in a discharge stage; wherein the programming stage comprises: programming the bit-cell of the memory array with a plurality of programming voltage pulses; wherein the discharge stage comprises: isolating a select line of the bit-cell of the memory array; and generating a programming voltage pulse to the bit-cell of the memory array; wherein the programming stage can be suspended to a suspend stage by a suspend command after the discharge stage; wherein the suspend command is received during one of the plurality of programming voltage pulse.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/905,838, filed Jun. 18, 2020, which is a continuation ofInternational Application No. PCT/CN2020/091037, filed May 19, 2020,both of which are incorporated herein by reference in their entireties.

BACKGROUND

The present disclosure relates to a control method and controller, andmore particularly, to a control method and controller of programsuspending and resuming for memory.

Semiconductor memories are widely used in various electronic devicessuch as cellular phones, digital cameras, personal digital assistants,medical electronic devices, mobile computing devices and non-mobilecomputing devices. A nonvolatile memory allows information to be storedand retained. Examples of the nonvolatile memory comprise a flash memory(e.g., NAND type and NOR type flash memory) and electrically erasableprogrammable read only memory (Electrically Erasable ProgrammableRead-Only Memory, EEPROM), etc.

In the nonvolatile memory, each memory element is configured to store acharge, voltage, or other electrical parameter to represent the data ina plurality of bit-cells (or memory elements), formed from floating-gatetransistors. Program operations typically occur in groups or pages ofmultiple memory cells. Read operations may occur in pages of memorycells or in smaller sets of memory cells. However, with the increasingnumber of cells in each page, the program operation may need to besuspended immediately upon receipt of the read command.

SUMMARY

It is, therefore, a primary objective of the present disclosure toprovide a control method and controller of program suspending andresuming for memory to improve over disadvantages of the prior art.

An embodiment of the present disclosure discloses a control method, fora memory array, the control method comprising programming the bit-cellof the memory array in a programming stage; and discharging the bit-cellof the memory array in a discharge stage; wherein the programming stagecomprises: programming the bit-cell of the memory array with a pluralityof programming voltage pulses; wherein the discharge stage comprises:isolating a select line of the bit-cell of the memory array; andgenerating a programming voltage pulse to the bit-cell of the memoryarray; wherein the programming stage can be suspended to a suspend stageby a suspend command after the discharge stage; wherein the suspendcommand is received during one of the plurality of programming voltagepulse.

An embodiment of the present disclosure further discloses a controllerfor programming a memory array, the controller for programming a memoryarray comprising a storage unit, configured to store a program code; anda processing unit, configured to perform the following steps:programming the bit-cell of the memory array in a programming stage; anddischarging the bit-cell of the memory array in a discharge stage;wherein the programming stage comprises: programming the bit-cell of thememory array with a plurality of programming voltage pulses; wherein thedischarge stage comprises: isolating a select line of the bit-cell ofthe memory array; and generating a programming voltage pulse to thebit-cell of the memory array; wherein the programming stage can besuspended to a suspend stage by a suspend command after the dischargestage.

These and other objectives of the present disclosure will no doubtbecome obvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of waveforms of a programming process fora memory array in the prior art.

FIG. 2 is a schematic diagram of waveforms of a suspending in aprogramming process for a memory array in the prior art.

FIG. 3 is a schematic diagram of waveforms of programming voltage pulsesin a programming process in the prior art.

FIG. 4 is a schematic diagram of waveforms of a programming process fora memory array according to an embodiment of the present disclosure.

FIGS. 5A and 5B are schematic diagrams of waveforms of a programmingprocess for a memory array according to embodiments of the presentdisclosure.

FIG. 6 is a schematic diagram of a programming process 60 for a memorysystem according to an embodiment of the present disclosure.

FIG. 7 is a schematic diagram of a memory system 70 according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

Certain terms are used throughout the description and following claimsto refer to particular components. As one skilled in the art willappreciate, manufacturers may refer to a component by different names.This document does not intend to distinguish between components thatdiffer in name but not function. In the following description and in theclaims, the terms “include” and “comprise” are used in an open-endedfashion, and thus should be interpreted to mean “include, but notlimited to.” Also, the term “couple” is intended to mean either anindirect or direct electrical connection. Accordingly, if one device iselectrically connected to another device, that connection may be througha direct electrical connection, or through an indirect electricalconnection via other devices and connections. “Roughly” means thatwithin the acceptable error budgets, those skilled in the art can solvethe technical problem within a certain error budgets, and basicallyachieve the technical effect.

While many embodiments are described herein, at least some of thedescribed embodiments facilitate program suspend/resume operations foran electronic storage device. In other words, a programming (or otherequivalents) operation that is being processed at non-volatile memory(NVM) may be suspended, either temporarily or permanently, in order toallow one or more other memory access operations (e.g., read, erase,partial program, etc.) to be processed at the NVM. As used herein, theterm “program operation” includes any operation to persist a value(digital or analog), or to persist a state which represents a value, onthe NVM. Some examples of other programs (or equivalents) operationsinclude, but are not limited to, burning, storing, writing, and settinga persistent value on the NVM. References herein to a program operationare inclusive of other equivalent or similar operations. Referencesherein to “suspending” are inclusive of other equivalent or similarterms, including, but not limited to, pausing, interrupting, queuing,and delaying.

A memory includes a memory array, including many pages of memoryelements. Each memory element is configured to store a charge, voltage,or other electrical parameters to represent the data. However, with theincreasing number of cells in each page, the programming time isincreasing, too. Therefore, the gap in idle in which the memory canserve the read command between each programming command is decreasing,and it is a problem that there is a need for a suspend command when thememory is executing programming command.

More specifically, FIG. 1 is a schematic diagram of waveforms of aprogramming process for a memory array in the prior art. As can be seen,a programming process comprises a plurality of programming voltagepulses in a plurality of programming stages, wherein the voltages of theplurality of programming voltage pulses are increased by the value ispp.Moreover, a verification stage is required to verify whether theprogramming is successful or not.

In other words, the program process may be performed using incrementalvoltage pulses, which incrementally increase the voltage level of valueto each voltage pulse, which increases the voltage level in value ofispp to store logic 0 or 1 in the bit-cell of the memory array untilpassing the verification. If then the verification fails, anotherprogramming voltage pulse with a higher voltage level is applied toprogram the bit-cell of the memory array.

In addition, the program suspending operation may be performed tosuspend a program (or write or other equivalents) operation on a givenpage of memory elements in order to read data from one of the memoryelements as the group of bit-cells of the memory array is programmed. Aprogramming voltage pulse count corresponding to the current programoperation is stored before suspending the program operation, so as tomake the memory array idle, which may serve the interrupted command,such as read command, and then continue to the programming stage,wherein the voltage level of the programming voltage pulse is based onthe programming voltage pulse count stored before the suspending.

FIG. 2 is a schematic diagram of waveforms of a suspending operation ina programming process for a memory array in the prior art. As can beseen, a suspend command received when the programming process isperforming, the memory array will serve the read request to other pages,and then resume to continuously the programming process.

However, when the programming process is suspended during oneprogramming voltage pulse, the resume of the program process may causethe programming channel to negative. In other words, regarding thenormal program, those threshold voltages Vt of the bit-cell are leftshift in time. As a result, holes will be accumulated in the channel andalso the charge trap layer. Moreover, the longer of the suspend timewould cause the more accumulating, which makes the bit-cell to be moreeasy to pass the first verification after resuming, even if the bit-cellis not programmed well.

On the other hand, if the read command is in a queue and performed afterthe programming process finishes, the read time will be pended until apage is finished the programming and verification. Therefore, the readlatency will be increased as the number of bit-cells of the pageincreases.

For example, FIG. 3 is a schematic diagram of waveforms of programmingvoltage pulses in a programming process in the prior art. As shown inFIG. 3, a suspend command received by the memory array, the firstverification after resuming is easy to pass because the thresholdvoltages Vt is shifted (shown in dot line) comparing with the thresholdvoltages Vt without suspending (shown in bold line.) This will make theread after the program to have more fail bits.

Different from the prior art, a control method of the present disclosureperforms the programming process for the memory array by inserting adischarge stage, which follows a programming stage, when the memoryreceives a suspend command in the programming stage. Thereby, the falseerror rate in the programming process is improved.

More specifically, please refer to FIG. 4, which is a schematic diagramof waveforms of a programming process for a memory array according to anembodiment of the present disclosure. As can be seen, the clean voltagepulse, which follows one programming voltage pulse, is impulsed to thememory array, and then the memory array transfers the programming stageto the suspend stage to serve other memory requests.

Practically, the voltage of the clean voltage pulse and its pulse widthmay be adjustable according to different utilization scenarios. In anembodiment, the voltage of the clean voltage pulse and its pulse widthmay be a fixed value by pre-determining, calibration, determined by amapping table, or adjusted accordingly to fit the practical scenario,which are corresponding to the voltage, the current, the temperature,the age or their combination thereof. Those skilled in the art may makemodifications of the decision rule and alterations accordingly, and notlimited herein.

To implement the requirements of generating the clean voltage pulse,FIG. 5A illustrates a schematic diagram of waveforms of a programmingprocess for a memory array according to embodiments of the presentdisclosure. As shown in FIG. 5A, the bottom select gate line is enabledin the discharge stage, which may release the holes and prevent thebit-cell from mis-programmed.

As can be seen, the interface of a bit-cell of the memory arraycomprises a top select gate line, a bottom select gate line, acharge-trapping line, a common-source line, and a p-well line. In theprogramming stage, the programming waveform is inputted to store data inthe form of logic 0 or logic 1. However, the interface of the memoryarray is not limited hereinabove, and those skilled in the art may makemodifications and alterations according to the memory array in the wholesystem.

In addition, FIG. 5B illustrates a schematic diagram of waveforms of aprogramming process for a memory array according to embodiments of thepresent disclosure. As shown in FIG. 5B, the bottom select gate line maybe enabled early to the end of the programming stage. That is, thedischarge stage may be shortly overlapped with the programming stage, tosave the transient time from the programming stage to the suspendedstage.

The operation of the programming process may be summarized to aprogramming process 60, as shown in FIG. 6. The programming process 60comprises the following steps:

Step 600: Start.

Step 602: Generating a plurality of programming voltage pulses toprogram the bit-cell in the programming stage, and performing theverification of the bit-cell in the verification stage.

Step 604: Generating the clean voltage pulse to the bit-cell whenreceiving a suspend command during a programming voltage pulse.

Step 606: Suspending the programming process, and transferring to thesuspend stage.

Step 608: Resuming the remaining of the programming process when otherrequests are finished.

Step 610: End.

In Step 602, the programming process 60 may be modified to have averification stage to follow a plurality of programming stages insequence. For example, in an embodiment, the programming process 60 maycomprise a first programming stage, a second programming stage, andfollowed by a verification stage.

In Step 604, the suspend command may modified to be queued after oneverification of a programming voltage pulse is finished; that is, thesuspend stage may be transferred from the programming stage or theverification stage. However, in Step 608, the remaining of theprogramming process should be performed continually. For example, if thememory array is suspended in the programming stage, then the remainingof the programming process starts with a verification stage in Step 608;if the memory array is suspended in the verification stage, then theremaining of the programming process starts with a programming stage inStep 608.

In addition, In Step 604, the clean voltage pulse may be generated by adummy programming voltage pulse, a dummy programming command, or otherway, which may discharge the holes to the bit-cell in the programmingprocess being suspended for the memory system.

The detailed operations of the programming progress 60 may be referredto the foregoing description, which is not narrated herein for brevity.

FIG. 7 is a schematic diagram of a memory system 70 according to anembodiment of the present disclosure. The memory system 70 includes amemory array 72, which is configured to store data in the form of logic0 or logic 1, and a controller 74, which is configured to receiveexternal commands and to toggle the waveforms to control the memoryarray 72. The bottom select gate line is enabled by the controller 74toggling the waveforms or receives an external command. In anembodiment, the controller 74 may comprise a processor and a storageunit. The storage unit may store a program code to instruct theprocessor to perform the function of toggling the waveforms of thepresent disclosure. In addition, the processor may be a processing unit,an application processor (AP) or a digital signal processor (DSP),wherein the processing unit may be a central processing unit (CPU), agraphics processing unit (GPU) or a tensor processing unit (TPU), andnot limited thereto. The storage unit may be a memory, which may be anon-volatile memory, such as an electrically erasable programmableread-only memory (EEPROM) or a flash memory, and not limited thereto.

In an embodiment, the memory system 70 may generate the programmingwaveform in discharge stage by generating a dummy programming command.In an embodiment, each of the programming voltage pulse may be followedby the dummy programming command. Notably, the present disclosure is notlimited to generating a dummy programming voltage pulse to the bit-cellof the memory, and those skilled in the art may discharge the bit-cellappropriately, for example, by enabling the bottom select gate line, orcombine the advantages of the methods mentioned above. The method ofcontrolling is known to those skilled in the art, which is not narratedherein for brevity.

In addition, the usage as the memory is suspended is not limited toreading. In fact, those skilled in the art may, according to differentutilization scenarios, substitute the read command and the readoperation with other memory access requests and operations correspondingto the other memory access requests respectively.

Notably, the embodiments stated in the above are utilized forillustrating the concept of the present disclosure. Those skilled in theart may make modifications and alterations accordingly, and not limitedherein. Hence, as long as a discharge stage is inserted after theprogramming stage to avoid holes accumulated to the bit-cell of thememory array in the programming process being suspended for a memorysystem, the requirement of the present application is satisfied.

In summary, by avoiding holes accumulated to the bit-cell in theprogramming process being suspended for a memory system, the controlmethod and controller of program suspending and resuming for memory ofthe present application have advantages of reducing the fail bit countsin the programming process, which may increase the robustness of thememory.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the disclosure. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A memory system, comprising: a memory cell array;and a controller coupled to the memory cell array and configured to:control applying a first program voltage to a word line to programmemory cells in the memory cell array, the memory cells being coupled tothe word line; and in response to receiving a suspend command, controlapplying a positive bias discharge voltage to the word line afterapplying the first program voltage.
 2. The memory system of claim 1,wherein the discharge voltage releases holes accumulated at the memorycells.
 3. The memory system of claim 1, wherein the first programvoltage is higher than the discharge voltage.
 4. The memory system ofclaim 1, wherein the suspend command comprises a read command.
 5. Thememory system of claim 1, wherein the controller is further configuredto, in response to completion of an operation caused by the suspendcommand, control applying a second program voltage to the word line. 6.The memory system of claim 5, wherein the second program voltage ishigher than the first program voltage.
 7. The memory system of claim 5,wherein the controller is further configured to, in response to thecompletion of the operation caused by the suspend command, controlapplying a verify voltage to the word line before applying the secondprogram voltage.
 8. The memory system of claim 1, further comprising aselect gate line coupled to the memory cell array, wherein thecontroller is further configured to, in response to receiving thesuspend command, control applying a positive bias select gate linevoltage to the select gate line.
 9. The memory system of claim 8,wherein the discharge voltage ramps up at a same time as the select gateline voltage.
 10. The memory system of claim 8, wherein the dischargevoltage ramps down before the select gate line voltage.
 11. A method forprogramming a memory cell array, comprising: applying a first programvoltage to a word line to program memory cells in the memory cell array,the memory cells being coupled to the word line; and in response toreceiving a suspend command, applying a positive bias discharge voltageto the word line after applying the first program voltage.
 12. Themethod of claim 11, wherein the discharge voltage releases holesaccumulated at the memory cells.
 13. The method of claim 11, wherein thefirst program voltage is higher than the discharge voltage.
 14. Themethod of claim 11, wherein the suspend command comprises a readcommand.
 15. The method of claim 11, further comprising, in response tocompletion of an operation caused by the suspend command, applying asecond program voltage to the word line.
 16. The method of claim 15,wherein the second program voltage is higher than the first programvoltage.
 17. The method of claim 15, further comprising, in response tothe completion of the operation caused by the suspend command, applyinga verify voltage to the word line before applying the second programvoltage.
 18. The method of claim 11, further comprising, in response toreceiving the suspend command, control applying a positive bias selectgate line voltage to a select gate line coupled to the memory cellarray.
 19. The method of claim 18, wherein the discharge voltage rampsup at a same time as the select gate line voltage.
 20. The method ofclaim 18, wherein the discharge voltage ramps down before the selectgate line voltage.